1. Field of the Invention
The present invention relates to an electro-magnetic fuel injector for supplying fuel to an internal combustion engine, and more particularly to a method for adjusting the injection quantity of fuel in the producing step thereof.
2. Description of the Prior Art
The conventional electromagnetic fuel injector of this type is provided with a needle valve which is reciprocally accommodated within a valve body, and an electromagnetic actuator for moving the needle valve to its open position, as shown in Japanese unexamined patent publication No. Sho 62-17365, for example.
The electromagnetic actuator includes a movable core which moves with the needle valve, and a fixed iron core around which an electromagnetic coil is wound. Into this iron core is inserted an adjust pipe in the moving direction of the needle valve. This adjust pipe serves as a fuel passage. The tip end of the adjust pipe is opposed to the movable core through a spring which continuously pushes and biases the needle valve in the direction of its closed position.
Upon the energization of the fixed iron core of the electromagnetic actuator, the movable core is attracted by the fixed iron core against the biasing force of the spring, and the needle valve moves to its open position so that fuel passes a nozzle hole formed in the valve body and is injected therefrom.
The injection quantity of fuel is varied in accordance with the opening and closing speed of the needle valve, which depends on the attracting force of the electromagnetic actuator and the biasing force of the spring. Therefore, conventionally, the compression quantity of the spring, that is the biasing force thereof is controlled by adjusting the position of the adjust pipe with respect to the movable core thereby to obtain a desired fuel injection quantity.
By caulking an outer peripheral portion of the fixed iron core after the above described adjustment, the adjust pipe is unmovably fixed to the fixed iron core thereby to set the injection quantity of fuel.
However, the above described conventional adjustment has a problem that the biasing force of the spring is apt to be undesirably varied during caulking of the fixed iron core or during running in the obtained electromagnetic fuel injector by electrifying the electromagnetic actuator and reciprocating the needle valve. Namely, the adjust pipe is comparatively freely movable in its axial direction before caulking. But, this adjust pipe is displaced due to the shock of caulking to vary the biasing force of the spring. This displacement of the adjust pipe can be considered to be resulted from that the outer periphery of the fixed iron core is caulked at a time to plastically deform and unequally expand the fixed iron core in an axial direction of the adjust pipe. And during running in, the spring is deformed to its more stable posture to vary the biasing force of the spring. This undesirable variation in the spring biasing force disenables the accurate adjustment of the injection quantity, and accordingly the injection quantity of the injector is frequently scattered from each other.